Convicted Bosnian-Croat war criminal Slobodan Praljak died of cyanide poisoning, Dutch officials said on December 1.

Dutch prosecutors said toxicological tests found that "Praljak had a concentration of potassium cyanide in his blood" that resulted in heart failure.

The 72-year-old Praljak stunned the International Criminal Tribunal for the former Yugoslavia (ICTY) on November 29 when he drank from a vial moments after a UN appeals judge upheld his 20-year sentence on war-crimes charges.

He died shortly afterward.

It remains unclear how Praljak obtained the poison.

A former commander of Bosnian-Croat forces in Bosnia-Herzegovina's 1992-95 war, Praljak was convicted in 2013 of crimes including murder, persecution, and deportation for his role in a plan to carve out a Bosnian-Croat ministate in Bosnia in the early 1990s.

He was one of six Bosnian-Croat defendants in court on November 29 to hear rulings on the appeal of their sentences at the ICTY.

Croatian political leaders seized upon Praljak's suicide as evidence of the failings of the war crimes tribunal, which was in the process of handing down its final judgment on November 29 before shutting down.

Conservative Prime Minister Andrej Plenkovic on November 30 voiced outrage at Praljak's death, describing his suicide as "an act showing a profound moral injustice" and saying that the verdict was "unacceptable."

Croatian President Kolinda Grabar-Kitarovic left a summit of female political leaders in Iceland, and the parliament broke off a session in the wake of the events in the tribunal.

Croatian lawmakers held a moment of silence for Praljak and the war victims on November 30, saying, "Let the death of General Praljak be the last act of the war."

Besides Praljak, the other five defendants included Bosnian Croat leader Jadranko Prlic, who appealed his 25-year term imposed by the court in The Hague, and four others, who are also appealing long prison sentences ranging from 10 to 20 years.

Before the November 29 hearing was halted, Prlic had also had his 25-year jail term upheld.

Prlic had been found guilty of being part of a criminal enterprise by the wartime Croatian government of late President Franjo Tudjman, to create an ethnically pure state.

Judges upheld that key finding, despite Croatian officials having denounced it and calling for it to be overturned.

Meanwhile, the U.S. Embassy in Sarajevo called the court’s verdict an "important step toward holding to account those individuals responsible for the tremendous suffering of the people" of Bosnia.

It also urged all parties to respect the verdict and "rededicate themselves to the continued reconciliation and peaceful coexistence essential to the future of a stable, secure" Bosnia.

The appeals hearing comes a week after the judges sentenced former Bosnian Serb military commander Ratko Mladic to life in prison.

It marks the end of two decades of work by the court, which was set up in 1993 at the height of the Balkans conflicts to prosecute Europe's worst atrocities since World War II.

With reporting by AP, Reuters, and bbc.com

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